From: Anthony J Sequeira (asequeira@internetworkexpert.com)
Date: Sat Oct 25 2008 - 02:57:26 ARST
The Layer 2 QoS markings may be generically termed Class of Service (CoS)
markings. In both ISL and 802.1Q frames across the trunk, there are three
bits reserved for the CoS marking.
The Cisco IP Phone is acting like a Layer 2 switch. Taking traffic from the
PC and the phone itself and trunking this traffic to the Catalyst switch
with CoS markings. By default the phone marks the VoIP traffic with a CoS of
5. This is the highest value Cisco recommends for marking traffic. Values 6
and 7 are reserved for network device usage.
Warmest regards,
Anthony J. Sequeira, CCIE #15626, CCSI #23251
Senior CCIE Instructor
asequeira@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-224-8987
Outside US: 775-826-4344
On 10/24/08 11:38 PM, "mark.chandra@gmail.com" <mark.chandra@gmail.com>
wrote:
> Hi guys,
>
> Just want to make sure my understanding about layer 2 qos.
>
> Layer 2 packet that we should call it frame, don't have tos bit in their
> frame. So Qos that Ieee called it 802.1p qos bit only can be carried by isl
> and dot1.q frame, is that correct?
>
> So, when I have a switchport connected to cisco ip phone that in default will
> forwarding frame with cos of 5. The switch port have to be a trunk, cause if
> not, isl or dot1q cannot carried the tos. Is that right?
>
>
> Can anybody correct me if I'm wrong.
>
> Thanks a lot guys
> Sent from my BlackBerry. wireless device from XL GPRS/EDGE/3G network
>
>
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>
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